The present invention relates to a sensor device for detecting wetting of a windshield.
German Patent No. 197 01 258 describes a sensor device that operates according to an optoelectronic principle for controlling wash/wipe systems for automotive windshields. The sensor device has multiple transmitters and at least one receiver for injecting and outputting via a coupling means a defined radiation into and out of the windshield whose wetting due to moisture or soiling is to be measured. The radiation is completely reflected at least once in the windshield on the (dry) surface of the windshield due to the injection angle and finally is output again to a receiver at a predetermined location. Total reflection is prevented by wetting of the surface of the windshield (air, water, ice, dirt, fog, etc.), resulting in wetting-dependent radiation losses due to output of a portion of the radiation from the original beam path, e.g., due to water droplets.
The diminished radiation detected by the receiver is outputted as a sensor signal to a signal processing arrangement, where it is analyzed with regard to controlling a wash or wipe system for an automotive windshield, for example. A controller controls the wiper motor in continuous or interval wiping mode as a function of the sensor signal analyzed.
According to German Patent No. 197 01 258, the transmitters are arranged concentrically around the receiver on the coupling means or concentrically in sections, the coupling means having a circular or toroidal design. Thus, a circular base area is spanned by transmitters, receivers and coupling means. For this reason, the sensor, i.e., the sensor casing, is in the form of a round cylinder.
The sensitive area of the sensor is defined by the sum of the measuring ranges of the windshield located approximately between a transmitter and the respective receiver, i.e., the one receiving the radiation. The measuring range is understood to be the range on the wettable side of the windshield within which the transmitter radiation is completely reflected in the absence of wetting, and therefore the transmitter radiation can be outputted more or less in the measuring range because of wetting of the windshield.
One disadvantage here is the circular base area defined by the transmitters, receivers and coupling means and the round cylindrical sensor casing, leading to a relatively great extent of the sensor and its contact area on the windshield and therefore making the sensor noticeable and causing interference for the driver of the vehicle when it is mounted within the wiping area on the windshield, as is customary today.
Another disadvantage here is the small proportion of sensitive area relative to the base area of the sensor, i.e., its contact area. This is due to the fact that with a predetermined number of transmitters, e.g., eight, the non-sensitive areas between the transmitters arranged on the outer perimeter of the base area are large, usually much larger than the sensitive areas.
To increase the size of the sensitive area, a great number of transmitters could be used. However, then the sensor would be more expensive without eliminating the disadvantages of the extent, i.e., contact area, of the sensor.
The sensor device according to the present invention has the advantage that the images of the transmitter and receiver as optical elements projected onto a plane parallel to the windshield form the corner points of a parallelogram or an isosceles triangle. The ratio of sensitive area to base area is increased by this arrangement of optical elements.
Due to the reduced base area, the outside dimensions of the sensor on the windshield and thus its contact area are likewise reduced. It is especially advantageous that due to the trapezoidal base area, rectangular outside dimensions of the sensor casing are selected, so that the base area can be arranged in the contact area with optimal utilization of the latter. In addition, a rectangular contact area, i.e., casing, is less expensive to manufacture.
The arrangement of the transmitters and receivers as a parallelogram is especially advantageous, such that two transmitters or two receivers are arranged at the opposite corner points. Thus four measuring zones, i.e., sensitive areas, of the sensor are implemented with only two sensors and two receivers by using transmitters whose transmitter light is bundled and deflected in two directions. The accuracy of the sensor in detecting wetting of the windshield is thereby greatly improved. This doubles the sensitive area in comparison with conventional transmitters emitting radiation to only one receiver.
It is also advantageous that the distances between the transmitters and receivers and thus the sides of the parallelogram are the same length. This converts the parallelogram to a rhombus. In particular, the distances are defined by the choice of only total reflection of the transmitter radiation in the windshield before the radiation is detected by a receiver. Consequently, the distances are minimal and thus the sides of the base area are also minimal.
It is likewise advantageous that the angles between the sides of the base area can be varied, and thus the base area can be adapted to the outside dimensions of the sensor and vice versa. For example, if only a narrow rain sensor can be used because of the automobile manufacturer""s requirements or the specifics of a given vehicle, smaller acute angles can be selected accordingly without any great effort until the extent of the base area can be optimally integrated into the outside dimensions of the sensor casing.
Consequently, it is especially advantageous for the transmitters and receivers to be arranged within the contact area of the sensor device, with the base area being optimally integrated into the contact area while at the same time the ratio of the sensitive area to the base area is increased. This yields an inexpensive sensor with small outside dimensions.